Molding apparatus



\ June 16, 1942. c NQCAR 2,286,994

MOLDING APPARATUS Filed Feb. 27, 1941- 3 Sheets-Sheet l INVENTOR EdwardC. Nocar j 'z mnh ATTORNEYS gormations on and bosses, provided toPatented June 16, 1942 UNITED STATE ENT oFFlca 2,386,994 Momma APPARATUSward C. Nocar,

Cleveland, Ohio, assignor to.

The Permold Company, Cleveland, Ohio, a cornotation of Ohio ApplicationFebruary 21, 1941, Serial No. swir s 12 Glaiml.

This invention relates to molding apparatus,

made in sand molds.

The internal structure of aluminum alloy pistons and the like andpistons formed primarily of aluminum alloy with Accordingly, the coresfor casting such pistons may have numerous shapes or coations. Mostlight metal or aluminum alloy r pistons do have lateral extensions orbosses on the inside ofthe skirt to receive the connecting rod pins.Frequently, the pistons have other lateral the inside or the skirt, suchas ribs strengthen or balance the structure. These lateral extensionsinteriorly oithe piston, being i rmed by the core. require that thelatter be contracted or collapsed and withdrawn in sections. Usually thecomposite or sectional core of a piston mold includes a central sectionand lateral or outer sections. The practice is to first withdraw thecentral sections from a casting, after which the outer or lateralsectures.

than pistons ferrous metal inserts. therein, may have widely variantinternal strucbinationwith a m for automatically withdrawing the coresections rapidly. from a pieton casting and for rapidly reassembling thesections in readiness for a succeeding casting operation.

I for a permanent Another object is to provide a sectional core mold andactuating mech therefor which I the core from a casting overpredetermined paths so as to avoid engagement between the coresectionsand casting during the withdrawal or the core. 1

Another object anism for a multi-part core which is so interconnectedthat by the movement of a single power-driven actuating hi all of thecore sections can be moved into and out of casting posh tion. Morespecifically, the invention aims to provide a sectional core for apiston mold in which one or more of they side core sections are mountedon the central core section and ar ranged to move to clear the lateralprojections tions are moved serially or simultaneously into the spacevacated by the central section so as to clear the projections on theinside of the piston skirt and are then withdrawn axially from thepiston casting. This withdrawal of the several core sections and thereofto prepare the apparatus for the next casting operation requiresconsiderable time and dexterity on the part f the operator it performedby hand. The faster the core sections can be withdrawn from a pistoncasting and then reassembled in preparation for the next castingoperation, the more rapidly the cyclic casting operation can beperformed. Consequently the production of the mold is increased by acore that can be quickly withdrawn from a casting and reassembled.

It" is therefore the principal oblect of the invention to provide animproved molding apparatus having a sectional or multi-part core incomthe subsequent reassemblingon the inside or the piston, and in whichthe several core sections are so interconnected that they can besuccessively moved into the center of the piston by a single powermeans.

Certain types of pistons have inwardly extend.- ing projectionscompletelyaround the shirt on the inside thereof. For casting pistons ofthis type a core must be provided in which all sections forming theskirt can be contracted or drawn inwardly so as to clear the lateralpro- .jections on the skirt. This invention is particularly suited tothe design of such cores and one of the principal features of thisdevelopment is the provision of a five part core which is adapted toform a completely circumferential ring around the inside of a pistonskirt.

Numerous structural improvements are incorporated in the apparatus,including means for pivotally mounting outer sections of the core sothat the core movement is guided by pivots and confined to predeterminedpaths; an arrangement of counterweights for balancing the core sectionsand for normally holding the core sections in assembled positions; thecombination of pivotally mounted side core sections and a cam movablewith the central core section for guiding the movement of the side coresections; and a lost motion connection for actuating certain of the coresections after a predetermined movement of a difierent'core section.Other objects I and advantages will become apparent from the followingdetailed description of a suitable emthdraws the-several sections of isto provide actuating mech- .bodiment of the invention made inconnectionwith the accompanyingdrawings, in which:

Figure 1 is a front elevational view of the molding apparatus, partly insection and with parts.

broken away, showing the mold sections and core assembled together inreadiness for casting;

Fig. 2 is a fragmentary vertical sectional view mounted on the supportmeans for the central section tilted toward one another so as to clearthe inwardly extending or lateral projections formed interiorly of thepiston;

Fig; 5 is a-sectional detail taken substantially on the line 5.--5 ofFig. 3;

Fig. 6 is a sectional detail taken substantially on the line 6-6 of Fig.4; and

Fig. 7 is a vertical view with parts removed and with parts broken away,showing the final stage in the withdrawal of thecore sections from thecasting cavity.

In the description of the invention like parts have been indicated bythe same reference numerals in the several figures. The apparatus ingeneral ismore fully described in the copendin'g application Serial No.380,695 filed February 26, 1941, of Sidney W. Jackson, and featuresdescribed but not claimed herein are reserved and claimed in thatapplication. Preferably, the mold comprises a supporting structureincluding uprights I which ,may rest" on a suitable founda tion 2 andare preferably formed of iron or steel. A table or bed 3, which may bean iron or steel casting, is mounted in a generally horizontal positionon the upper ends of the uprights I.

Slidably supported on ways 4 of the table or bed 3 are mold sections 5and 6 which are movable toward and away from one another and have theirmeeting faces suitably formed or receased to define the exterior-of thepiston or other article to be cast, indicated at A, and also suitablepassages for introducing molten metal into the casting cavity.

Levers 9 pivoted at 9 to the bed 3 are connected by adjustable linkagesf9 to the mold sections 5 and 6 so that the latter can be moved towardand away from one another and positioned on the ways 4'in definiterelation with respect to one another and the sectional core to be laterdescribed.

Core pins l5 are slidably mounted in the mold sections 5 and 6 and havetapered ends which project into the casting cavity when the mold isassembled in pouring position to form aligned apertures I! in the pistonA. These passages are later machined to receive a, connecting rod pin.The pins l5'have heads which limit the movement of the pins into thecasting cavity and each of the pins is formed with rack teeth engaged bythe toothed end of a vertically disposed rod 20 rotatably mounted in thecorresponding mold section. Handles 2| secured on the upper ends of therods 20 enable the latter to be rotated for movement of the pins l5 intoand out of the casting cavity.

A ring-like base member 22 is formed with a circumferentially extendingradial flange 23 which seats on a depressed shoulder 24 of the table 3.-The base 22 extends downwardly through an opening 25 in the table and acylindrical passage or opening 26 is formed in the base member toreceive the multi-part core,

The core comprises a central section 96 and outer sections 29 and 29,the latter being disposed on opposite sides of the center section andhaving recesses 39 which form inwardly. directed or laterally extendingpiston pin bosses 3! on the inside of the skirt of the piston A. Thesebosses'have 1:1;81'8111 the openings I! defined by the core pins- Thecentral section 96 of the core-is mounted on a support 99 secured on theupper end of an actuating or power driven rod 33. This rod has a piston34 (Fig. 1) secured on its lower end and reciprocable in a cylinder 38secured by an upper end member 39 in an opening 3! formed in across'member 39 supported by the uprights I. The foundation 2 for theapparatus may be formed with a pit "to receive the lower end of thecylinder 35. The top endmember 39 and a bottom end member 49 on thecylinder 35 are connected by conduits 4| and 42, respectively, throughcontrol valves (not shown) to a suitable source of fluid or air underpressure. Thus, air or fluid under pressure can be introduced into thecylinder 35 either'above or below the piston 34 to force the same up ordown as desired to either raise or lower the rod 33 and the central coresection 99.

Supported on the cross member 39 is a bracket which has a verticallydisposed guide portion 49 engageable with one side of the support 99which slides therealong.

The mechanismjor supporting and actuating the outer core sections 29 and29 includes members 49 and 50 formed with T-slots,-into whichcorrespondingly shaped portions of the base of the core sections areinterfitted. Bolts 54, which extend throughy'the supports 49 and 50, are

threaded into the bottoms of the core pieces to secure the latter in theT-slots of the supports.

The support 50 for the core section 29 is tiltably carried by a pivotpin 91 and is disposed between the ends of a pair of spaced parallelpivoted members or arm 99, which receive the pivot pin 91 to support thesame. The arms 59 are pivotally supported on a pin 99 carried by abracket 90 secured to the underside of the table or bed 3 at apointremote from the opening 26 in the mold base. Desirably, a separatorBI is received on the pivot pin 59 between the .arm members 39 and issecured to the latter by means of a bolt 92, so that the separatorrotates with the arms. A counterweight 93 is mounted on the end of anarm 64 threaded into the sepaii and balances the weight of the coreratorsection 29 and the mechanism latter,

for supporting the so that the core is normally held thereby in itsuppermost position and the raising and lowering of the core section isfacilitated.

A depending extension 99 of the core support 59 has secured in its lowerend or foot a transverse guide pin 96 which extends into a slot 61formed in a cam member 69 secured to the cross member 99-, The foot ofthe extension 65 has a toe portion 99 which is directed toward the pathof the-support 99 for the central core section. The support 99 has aknob-like portion 19 which bears against one side ll of the extension 65as the central core section 99 is lowered b the downward movement of thepiston 34. As the central core section approaches its lower limit ofmovement, the knob it of the support 99 bears against the curved toeportion '99 of the extension 65 on the support 50 and forces the toe tothe right, as viewed in Figs. 1 and 'I. This movement tilts the support50 and the mold section 29 in a counter-clockwise direction on the pivot91, thus freeing the core section from one of the wrist pin bosses-3| ofthe piston A, and moving the core section into the space vacated by thelowered central core section 95.

The upper end of the cam slot 61 has a horizontal portion it whichreceives the cam pin 65 when the core sections are in assembled position(Fig. 1). Accordingly, while the central core section 98 is beingwithdrawn from a casting, as will be later described, by the powerdevice 35, the outer core section 29 is positively held in its uppermostposition within the casting by the engagement of the cam pin 66 in thehorizontal portion the support mechanism for the core. section 29'istilted, the cam pin 69 is-in line with the downwardly extending portionof the cam groove 61, which controls the movement of the core sec tion29 cooperatively with the support members or arms 59 and restricts thedownward movement of the core section toapredetermined path.

The extension 69 of the support 59 is centrally slotted or cut away, asindicated at it, and receives a hook member or arm it which is mountedon a pivot pin it extending through the upper end of the cutaway portionof the extension and secured in the sides of the extension. The memberit hangs downwardly in the slot or groove and lower end or hook portion59 thereof is disposed slightly below the toe t9 and in the path ofthe'knob-iike portion 19 on the support 99. A weight 39 mounted on theend of an arnr 99 threaded into the upper portion of the memher it holdsthe latter against the knob ill on the support 99 during the lowering ofthe latter, so that when thesupport 59 and outer core section- 29 aretilted by the interengagement of the toe 59 and knob it, the hook it isretained in the path of the knob to be engaged by the latter. Since thehook it is below the end of the toe 69, the knob it does not engage thehook until after the guide pin 9% has been shifted into alignment ,withthe downwardly extending portion of the cam slot 9?. As the central coresupport 99 is drawn downwardly from the casting, the tilted core section29 is lowered simul-' taneously therewith by theinterengagement of thehook 18 with the knob i0. During this movement the outer core section 29is. guided over a predetermined path by the cam slot 6! in cooperationwith the pivoted arms 58. Thus, ob-

' jectionable contact between the core sectionand the lateral orinwardly extending projections on the skirt of the fresh casting isavoided.

The support 49 for the outer c re section 28 is pivotally mounted on apin 8 carried by a bracket 84 secured to the underside of the table orbed 3 adjacent the cylindrical opening 26 in the mold base. A dependingextension portion 85 on the pivoted support member 49 has a lower endwhich is bifurcated and straddles web 86 of the bracket 45. A pin 81journaled in the lower. ends of the bifurcated portion of the extension85 is received in a slot 88 formed in the web 86 and limits theoscillating movement of the support member 49 on the pivot 83. On theends of the pin 8? beyond the sides of the extension portion 85 of thecore support are struts or arms 89 which extend upwardly in it of thecam slot. When an oblique direction and across the path of the pivotpin' 51 which carries the support for the core section 29. The upperends of the strut arms 89 are formed with seats 99 engageable with theends of the pivot pin 51 asthe latter is lowered by the interconnectionof the parts with the piston 34. Weights 9| mounted on the ends areretained in correct position for engagement.

of the pivot pin 51' in .the seats 90 upon lowering of the outer coresection 29. After the pin 51 has engaged the arms 89, the latter arethereby forced downwardly-and to the left, which causes a shifting ofthe pin 81 in the slot 89 from'the right to the left, so that thesupport member t9 and the outer core section 28 are tilted in aclockwise direction to substantially the position illustrated in Fig. 7.In this position the core piece 28 has been freed from the casting sothat it clears the lateral or inwardly extending wrist pin boss 3| andis positioned in the space previously vacated by the central coresection 95 and the other outer core section 29.

This invention is particularly directed to the arrangement forsupporting a pair of lateral or side core sections 9? and 99 on the sameprime mover 0r actuator 99 as the central core section 96. The support99 is formed with an upwardly extending portion i139 which carries andis surmounted by the middle or central core section 96; the latterpreferably being of tapered form. The side core sections 9? and 99 haverecesses IIJI on their outer surfaces whichform inward- 1 extending ribs192 adjacent the bottom of the skirt'of the piston A. Similar groovesmay be formed in the core sections 29 and 29, if desired, so that therib nor may be circumferentially continuous around the inside of thepiston skirt. Bolts I99 secure the side core sections 91 and 98 to apair of tiltable supports I99 which.

are disposed on opposite sides of the upwardly extending support portioni9!) and are pivotally mounted on spaced parallel pins E which arecarried by guide plates or members I06. These guide members are disposedin spaced parallel relation to one another on opposite sides of theupright portion iflii of the support 99, and are cut away or slotted, asindicated at "ii, to straddle the support 99 to be guided by the latter.The slots I91 are of sumcient vertical extent to permit verticalmovement of the guide members 1081 with respect to the support 99 whilebeing restrained against lateral movement by engagement with thesupport.

A pin I 08 is secured in the portion I00 of the support 99 and extendsinto vertically .elongated slots I09 formed in the guideplates I06.Thus, the sidecore sections 91 and 99 may be simultaneously movedvertically with respect to the central core section 96 while pivotallysupported side core sections 91 and 99. the guide plates. I remainingstationary and the-pin I09 moving downwardly in the slots I09. When thecentral portion I00 of the support 99 moves downwardly between thefingers 0 so that cam surfaces 2 of such thickened portion of thesupport forces the fingers IIO apart to tilt thesupports I04 on the pinsI05. By this action the side core sec-.

tions 91 and 99 are drawn or tilted inwardly or toward one another tothe full line position illustrated in Fig. 4, thus freeing the same fromthe inside of the casting and withdrawing the' slots or recesses I 0|from the ribs I02.

displacement of the central and lateral cores or into the space vacatedby the descending central core support by the knob 19, the support 92bears laterally against the guide portion 49 of the bracket 49, thuspreventing side movement or of the actuating rod 99. After the initiallost As downward movement of the support99 is continued under theinfluence of the power actuated piston rod 33, the pin I00 seats in thebottoms of theslots I09 to thereby establish a positive connectionbetween the parts to draw the guide plates I06 carrying the side coresections 91 and 99 downwardly, thus lowering the central core sectionand side core sections simultaneously. It is to be noted that thetapered character of the central core section 96 provides suflicientclearance so that the side core sections 91 and 99 can be tiltedinwardly toward one another when the central core section has been onlypartially withdrawn from the piston casting.

In order to support the side core sections 91 and 99 to insure that theyare lowered only when positively drawn downwardly by the engagement ofthe pin I08 in the bottoms of the slots I09,

flexible elements or ropes S are secured to the guide plates or membersI06 at 6 and are carried thence upwardly over pulleys 0r sheaves Il1rotatably mounted in brackets H8 secured to the bed or table 3. WeightsI I9 are supported on the ropes or elements H5 and operate to exert acontinuous upward force on the members I09 so that the pin I08 seats inthe bottoms of the slots I09 except when the core is in assembledcondition.

In operating a mold of the character described.

the molten metal is poured into the casting cavity of the assembled moldshown in Fig. 1, the cavity being formed above the base 22 by the .moldsections 5 and 6 around the core sections 99, 91, 98, 29 and 29. Aftersolidification of the metal and when it is desired to withdrawn themulti part core from the casting, the operator introduces fluid or airunder pressure into the upper end of the cylinder 95 to force the piston39 downwardly. In this manner the support 99 carrying the central coresection 96 is lowered; The movement of the support'99 and the extensionI00 thereof operates to first tilt the lateral core sections 91 and 99toward one another to clear the rib I02 and to then withdraw the centraland lateral core sections simultaneously and as a unit. The withdrawalof the lateral core sections 91 and 99 is delayed bythe lost motion ofthe pin I09 in the slots I09 of the guide plates I06 until the taperedcentral core section 96 has been partially withdrawn. Thus a space orclearance is provided into which the. lateral core sections can betilted. After the central core section 96 and the lateral core sections91 and 98 have been withdrawn from the casting,

manner the core section 29 is withdrawn from the casting A through thespace previously occupied by the central and lateral core sections 99,91 and 99, the pin 96 being guided in the cam slot 91 to hold the coresection 29 and the support 50 therefor to a predetermined path ofmovement. After a second period of lost motion during which the outercore section 29 is withdrawn from the casting and the central andlateral core sections 99, 91 and 99 are further withdrawn, the pin 51 isengaged in the seats 90 of the arms 89, forcing the latter to the leftto the position shown by the full lines of Fig. '1. In this manner theouter core section 29 is tilted to the position illustrated in Fig. "1,so that it clears the lateral extensions on the inside of the casting. I

To reassemble the cor for the next casting operation the operatorintroduces airor fluid under pressure into the lower end of the cylinder35, thereby forcing the piston and rod 99 upwardly. The weights I I9serve to raise the guide plates ormembers I06 and the side core sections91 and 99 supported thereby. The upper limit of movement of the side orlateral core sections 91 and 99 is determined by a shoulder I20 formed,by areduced diameter portion of the cylindrical passage 26. Thisshoulder engages the upper ends of the tiltable supports I04 when theside core sections 91 and 99 have been moved to their uppermostpositions illustrated in Fig. 4. The knob 10, moving upwardly, permitsthe support 50 to be raised by the weight 93 to elevate the outer coresection 29 to its correct position with respect to the mold base 22. Asthe arms 99 are released by the pin 51, the weights 9| tilt the armsagainst the pins 99 and also tilt the support 49 on the pivot pin99 soas to move the outer core section 29 substantially. to its correctposition with respect to the mold base 22. The upward movement of thecore section 29 is guided by the -movable or pivoted members 59 and thepin 69 in the cam slot 91. A circumferential shoulder 94 on the outercore section 29 engages the bottom of the mold base 22 to limit theupward movement of the core section and the tapered central core section99 bears against the sides of the outer or lateral core sections 91 and99 to spread and support the latter in correct relation with respect toone-another, and to move the the cast articles and withdrawing thetiltled sectime in succession. First the side core sections aaaacoa 97and 98 are withdrawn through the space previously occupied by thecentral core section 96, and then the outer core sections 28 and 29 aresuccessively tilted into such space. The successive tilting andwithdrawal movements of the several core sections take placeautomatically under the influence of a single power actuated member andthe retracted core sections can be automatically reassembled intomolding positions by a simple reverse movement of the one prime mover orpower member. Hence, the core may be efficiently manipulated by a singleoperator without an extended period of training or instruction.Furthermore, the apparatus can be quickly and economicaly operated,thereby lowering the cost of production of the articles being cast,-while increasing the number of articles that can be made in a givenperiod of time.

The principles of the present invention may be utilized in various ways,numerous modifications and alterations being contemplated, substitutionof parts and changes in construction being resorted to as desired, itbeing understood that the embodiment shown in the drawings and describedabove is given merely for purposes of explanation and illustrationwithout intending to limit the scope of .the claims to the specificdetails disclosed.

What I claim is:

1. A piston mold core comprising a central section, a first pair ofouter sections, a second pair of outer sections, means supporting thecentral section and actuable to withdraw the same from a piston casting,means mounting the first pair of sections on the support for the centralsection, and means mounting the second pair of sections for tiltingmovement, said last means having lost motion connection with thesupporting means to tilt the sections of the second pair into the spaceformerly occupied by the central section after a predeterminedwithdrawal of the latter.

2. In a multi-section core for a permanent mold, a central section and asupport therefor actuable to withdraw the section from a casting, sidesections and means mounting the same on the support for movement withthe latter,

said mounting means having lost motion connection with the support toprovide for limited movement of the support in withdrawing the centralsection prior to movement of the side sections with the support, andmeans for actuating the support over a generally rectilinear path towithdraw the central section and the side sections sequentially from acasting.

3. In a multi-section core for a permanent mold, a central section and asupport therefor actuable to withdraw the section from a casting, sidesections and means mounting the same on the support for movement withthe latter, said ,mounting means having lost motion connection with thesupport to provide for limited movement side sections mounted on thesupport for limited movement relative thereto in the direction ofwithdrawal of the central section and also fortilting movement tofandfrom one another, means for actuating the support to withdraw thesections from a casting, and means secured to the side sections andengageable with the support during said limited relative movement totilt the side sections.

5-. In' a multi-section core for a permanent mold, a central section anda movable support therefor actuable to withdraw the section from acasting, a guide slidable on the support and means limiting the slidingthereof, a side section pivotally mounted on the slide for tiltingmovement, and means operable during sliding of the guide to tilt theside section.

6. In a multi-section core for a permanent mold, a central section and amovable support therefor actuable to withdraw the section from acasting, a guide slidable on the-support and means limiting the slidingthereof, a side section pivotally mounted on the slide for tiltingmovement, and co-acting cam parts on the support and side section whichbear against one another during sliding of the guide to tilt the sidesection.

'7. In a multi-section core for a permanent mold, a central section anda vertically movable support therefor, a guide slidable vertically onthe support and means limiting the movement of the guide. on the slide,a side section and means mounting the same on the guide for tiltingmovement, and means having connection with the guide and normally urgingthe same to its upper limit of movement on the support to retain theside section above the center section during raising of the support inassembling the sections.

8. In a multi-section core for a permanent mold, a central section and avertically movable support therefor, a guide slidable vertically on thesupport and means limiting the movement of the guide on the slide, apair of side sections and means mounting the same on the guide fortilting movement toward and away from one another, means connected tothe side sections and of movement to tilt the side sections together,

of the support in withdrawing the central section prior to movement ofthe side sections with the support and also including means actuable byrelative movement between the central section and the side sections totilt the latter toward one another during said limited movement of thesupport, and means for actuating the support over a generallyrectilinear path to withdraw the central section and the side sectionssequentially from a casting.

4. In a multi-section core for a permanent mold, a central section and asupport therefor actuable to withdraw the section from a castin andmeans having connection with the guide and normally urging the same toits upper limit of movement on the support to retain the side sectionstilted together during raising of the support in assembling thesections.

9. In a multi-section core for a permanent mold, a central section and-asupport therefor actuable to withdraw the section from a casting, a.guide slidable on the support in the direction of withdrawal of thecentral section, side sections disposed on opposite sides of the centralsection and pivotally connected to the guide for tilting movement, andco-acting cam parts on the support and side sections which bear againstone another during sliding of the guide on the support to tilt the sidesections toward one another as the central section is withdrawn.

10. In amulti-section core for a permanent mold,. a central section anda support therefor actuable to withdraw the section from a casting, aguide slidable on the support in the direction of withdrawal of thecentral section,

side sections disposed on opposite sides of"the central section andpivotally connected to the guide for tiltingmovement, co-acting camparts on the support and side sections which bear against one anotherduring sliding oi the guide on the support to tilt the side sectionstoward one another as the central section is withdrawn,

and pin and slot means interconnecting the guide and the support tolimit the relative sliding movement of the guide on the support.

11. In a permanent mold having a generally horizontal apertured base, amulti-section core comprising a central section and a support there-4for actuable for substantially vertical movement to raise and lower saidsection through the base aperture, a guide and means mounting the samefor movement in substantial parallelism with the movement of thesupport, a side section piv-K tral section prior to the side section,said upward urging means being yieldable downwardly to permit movementof the sections in unison below said limited independent verticalmovement.

12. In a permanent mold having a generally horizontal'apertured base, amultl-section core comprising a central section and a. support there foractuable for substantially. vertical movement to raise and lower saidsection through the base aperture, a guide and means mounting the samefor movement in substantial parallelism with the movement of thesupport, a side section pivotally mounted on the guide, means havingconnection with the guide and normally urging the same upwardly againstthe underside of the mold base to support the side section in raisedposition in the base aperture, means providing a limited slidingconnection between the support and the guide to permit limited verticalmovement of one independently of the other during assembly anddisassembly oithe core, whereby lowering the support withdraws thecentral section prior to the side section, said upward urging meansbeing yieldable downwardly to permit movement of the sections in unisonbelow said limited independent vertical movement, and means havingconnection with the side section and arranged to automatically tilt thelatter into space vacated by the central section prior to the movementof the sections in unison. a

EDWARD C. NOCAR.

